1. The Technical Field
The present invention is directed generally to a method and apparatus for controlling an engine capable of operating on more than one type of fuel. More particularly, the present invention is directed to a method and apparatus for optimizing the torque output of a compression ignition engine capable of operating on more than one type of fuel.
2. The Prior Art
Spark ignition engines capable of operating on gasoline, ethanol, and blends thereof are known in the art. Such engines are commonly referred to as flexible fuel (or flex fuel) engines. Some known control systems for these engines require selection of an engine control algorithm based on an anticipated fuel composition, for example, 100% gasoline or 15% gasoline and 85% ethanol (the latter of which is commonly referred to as E85). Other known control systems sense the composition of the fuel in the fuel tank and adjust the engine control algorithm accordingly. Yet other known control systems sense exhaust gas air-to-fuel ratio and adjust the amount of fuel being provided to the engine to bring the air/fuel mixture toward stoichiometric. Generally, the motivation behind these systems is to optimize the engine's emissions performance.
Compression ignition engines capable of operating on both diesel fuel and aviation kerosene (jet fuel) also are known in the art. Known control systems for such engines typically require the operator to manually select an engine control algorithm appropriate for either diesel fuel or jet fuel. One shortcoming of such prior art systems is that they require the operator to know or guess what fuel type is being supplied to the engine and manually adjust the engine control system accordingly. Another shortcoming of such prior art systems is that neither the diesel fuel algorithm nor the jet fuel algorithm may be particularly well-suited for controlling an engine being supplied with a blend of diesel and jet fuel or where the properties of the fuel being used are varying within their allowable specifications. Fuel blending is likely to occur any time fuel is added to a partially empty fuel tank through inattention, because the person filling the tank might not know what type of fuel is already in the tank, or because more of the type of fuel already in the tank is not available.